Piscivorous fish are size-selective predators. Although sizes of prey selectively ingested by piscivores traditionally have been measured in terms of prey length relative to predator length, the relationship between prey body depth (measured dorsoventrally) and piscivore mouth gape may be a more appropriate measure of prey size selection. In 2-d feeding trials with three sizes of largemouth bass Micropterus salmoides, I offered various sizes of shallow-bodied fathead minnows Pimephales promelas and deep-bodied pumpkinseeds Lepomis gibbosus in assemblages of one or both species. All sizes of predators preferred pumpkinseeds with body depths well below the maximum size ingestible. Small predators also preferred fathead minnows with body depths below the maximum size ingestible, whereas intermediate and large predators selectively ingested the largest fathead minnows offered. Largemouth bass never ingested prey of body depth greater than their own external mouth width. Although lengths of selectivel...